doble TDR900, User

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Doble TDR900 User Guide
72A-2612-01 Rev. A 09/06
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4.4.3 Arc Quench and Insulation
In all breakers there is a need, during the trip operation to extinguish any arc developed.
This may be achieved through:
•
Air blast
•
Oil
•
SF6
•
Vacuum
•
Some other means
The act of extinguishing the arc is related to the need to insulate the conductors.
Insulation is sometimes provided through the same means as arc extinction.
4.4.4 Breaks per Phase
As voltages increase, it becomes increasingly difficult to break current and quench the arc
produced through a single break. Multiple breaks are required in series to distribute a
reduced voltage across each break. Twelve or more breaks per phase may be found.
Consequently, such multiple breaks per phase units are higher voltage than “usual”
breakers, and became known as Extra High Voltage or EHV, breakers. The tank is
usually “live.” Thus, another name used for EHV breakers is “live tank” breakers.
As technology has progressed, the number of breaks per phase has been reduced, though
voltages have continued to increase. But the term of EHV for multiple breaks per phase
breakers is still common.
4.4.5 Capacitors and Resistors
Breakers with multiple breaks per phase use resistors and capacitors as dividers so each
breaking element will have equal transient voltage when tripping.
Line breakers can have so-called insertion resistors on close for dampening overvoltages
on close.
4.4.6 Independent Pole Operation
Each phase of breaker is also known as a pole. Usually the governing mechanism for
each phase, or pole, is operated centrally and the breaker acts as a unit. All phases should
be tested simultaneously.
In independent pole operation, each phase or pole, acts independently. Each phase may
be tested separately.